1. Field of the Invention
The present invention relates to an atmospheric pressure measuring apparatus and a method of measuring an atmospheric pressure.
2. Description of the Prior Art
An atmospheric pressure measuring apparatus includes a closed cavity with a deformable wall for detection of the absolute pressure. A sensor is placed in contact with the wall of the closed cavity. The closed cavity contains a predetermined amount of gas to hold a reference pressure therein. A variation in the atmospheric pressure around the closed cavity induces a variation in the volume of the closed cavity. The sensor is thus designed to detect the variation in the volume by sensing either the deformation or stress or strain on the wall of the closed cavity. The atmospheric pressure measuring apparatus enables detection of the atmospheric pressure based on a variation in the volume of the closed cavity.
The pressure inside the closed cavity is kept constant level so as to ensure the accuracy of detection of the atmospheric pressure in the atmospheric pressure measuring apparatus of this type. Pressure is always applied to the sensor. Accordingly, the sensor may suffer from generation of so-called creep. This results in deterioration of the accuracy of detection. A conventional atmospheric pressure measuring apparatus has another drawback. The wall of the closed cavity is required to have a reduced thickness so that the wall of the closed cavity deforms in response to the application of pressure. This makes the atmospheric pressure measuring apparatus fragile. Moreover, it is quite necessary to completely seal the closed cavity so as to keep the pressure constant. A high processing technique is required to produce the closed cavity.